Heretofore, there is known a tire which is provided with a circumferential groove extending continuously in the tire circumferential direction and provided in groove side walls with a plurality of radial grooves arranged along the longitudinal direction of the circumferential groove as disclosed in Japanese Patent Application Publication No. 2009-227222 (Patent Document 1). Such radial grooves likely cause turbulence to water flowing in the circumferential groove, and facilitate a separation of the water flow from the groove side walls of the circumferential groove. Further, the radial grooves acts as a resistance to air flowing in the circumferential groove, and reduce a resonance sound generated from an air tube formed by being surrounded by the circumferential groove and the road surface. Thus, the tire provided with the radial grooves has excellent drainage performance and noise performance.
However, when demolding the vulcanized tire from a vulcanization mold provided with protruding portions for forming the radial grooves, there is a possibility that the rubber of the side walls of the circumferential groove are damaged by being scratched or torn by the protruding portions.